webapp: introduce Laravel app under webapp/ for scene overlays

Replaces the per-scene HTML directories (landing/, loading/, game/,
desktop/, goodbye/, music-box/, music/) with a single Laravel app
serving every overlay over HTTP. Supervisord runs `php artisan serve`
on 127.0.0.1:1118 and the OBS scene JSON now references HTTP routes
instead of file:// URLs.

Highlights:
 - public/css/hud.css consolidates the duplicated HUD chrome,
   scanlines/vignette/flicker, terminal styling, and pulse keyframes
   that were copy-pasted across all seven scenes.
 - Blade partials own hud-strip, crt-overlays, obs-ws-scripts,
   camera-frame, screen-frame; the seven scenes extend a shared
   overlay layout.
 - Artisan commands (`rig:setup`, `rig:telemetry`, `rig:loading`,
   `rig:playlist`, `rig:cmd`) replace the shell scripts that wrote
   per-rig JSON snapshots. TwitchHelix + HardwareSnapshot services
   handle the work the bash + Python helpers used to.
 - ObsWsClient + MusicCommandController kill the 250 ms cmd.js poll
   in the music daemon: POST /cmd/{skip|prev|pause|resume} opens a
   short-lived Pawl WS, authenticates, and broadcasts mpd:cmd.
 - AudioController streams files from the configured music dirs so
   CEF can load tracks under the HTTP origin (Chromium blocks
   HTTP-origin pages from loading file:// media).
 - DataController serves /data/playlist.js (with ETag mtime cache)
   and /cover.jpg (no-store) so the existing overlays' window.__PLAYLIST
   and cover.jpg cache-bust pattern keeps working.

scripts/obs-webapp.supervisord.conf is the supervisord unit; install
to /etc/supervisor.d/obs-webapp.conf.
scripts/rewrite-scene-urls.py is a one-shot tool that rewrites
basic/scenes/Default_Stream_HUD.json from file:// to HTTP URLs.
basic/scenes/Default_Stream_HUD.json.pre-webapp is the rollback
artifact (made with OBS closed; full pre-migration state).

The seven old scene directories, vendor/, and the bash scripts are
still on disk pending visual verification; the next commit will
prune them.

webapp/resources/views/partials/hud-strip.blade.php

@@ -0,0 +1,27 @@
+@php
+    /** @var string $variant variant: 'live' | 'onair' | 'offair' */
+    $variant     = $variant     ?? 'live';
+    $label       = $label       ?? 'TRANSMISSION';
+    $idText      = $idText      ?? 'OPHI-118';
+    $signalGlyph = $signalGlyph ?? '▮▮▮▯▯';
+    $signalProfile = $signalProfile ?? 'normal';
+    $extraIdSlot = $extraIdSlot ?? null;
+@endphp
+<header class="hud hud--{{ $variant }}">
+  <div class="group">
+    <span><span class="led"></span>{{ $label }}</span>
+    @if ($extraIdSlot)
+      {!! $extraIdSlot !!}
+    @else
+      <span>{{ $idText }}</span>
+    @endif
+  </div>
+  <div class="group">
+    <span class="dim">SIGNAL</span>
+    <span id="signal" data-profile="{{ $signalProfile }}">{{ $signalGlyph }}</span>
+  </div>
+  <div class="group">
+    <span class="dim">UTC</span>
+    <span id="clock">--:--:--</span>
+  </div>
+</header>